The present invention relates to improvement in an electrically conductive rubber material used as a charging member for electrophotographic copying apparatus.
An electrophotographic copying apparatus operates by forming an electrostatic latent image on the surface of a photoreceptor, applying toner thereto to form a toner image, and transferring said toner image to a copying paper sheet. In this case, for production of electrostatic latent images, use has heretofore been made of the corona discharging system, which, however, raises such problems as ozone emission and use of high voltages. Thus, the recent tendency has been to avoid using the corona discharging system and there has been investigated a contact charging system in which the photoreceptor surface is charged by being contacted with a charging member made of electrically conductive rubber or the like.
In the contact charging system, however, the charging member is in contact with the photoreceptor surface, so that the bleeding of oil ingredient, such as a softening agent, plasticizer and the like, and the blooming of a cross-linking agent of the sulfur type on the electrically conductive rubber used as the charging member may damage a resin film on the photoreceptor surface and deform the copy image.
The rubber usually includes oily ingredients, such as a softening agent, plasticizer and the like, which is added to the rubber to lower the hardness thereof and to provide easier processing therefor. If, however, too much oil ingredient, of a softening agent and plasticizer, is added, some of the oil ingredient of the softening agent and plasticizer could microscopically bleed on to the rubber surface, though not visible to the naked eye. Therefore, in an electrophotographic copying apparatus, such a rubber material may cause contamination of or damage to the photoreceptor due to the bleeding of the oil ingredient of the softening agent and plasticizer as well as deformation of the copy image due to the contamination of the photoreceptor. Further, if a cross-linking agent of the sulfur type is used for the rubber, it bleeds microscopically on to the rubber surface like said oil ingredient of the softening agent and plasticizer to contaminate or damage the photoreceptor and to deform the copy image.